2. Field of the Invention
This invention relates to bearing shaft seals and more particularly to such a seal including an elastomeric seal body having a lubricant sealing portion and an improved dust sealing portion spaced axially from the lubricant sealing portion.
2. Description of the Prior Art
It is well known to provide lubricant seals between a shaft and a cylindrical housing within which the shaft is supported for rotation relative to the housing, with the seal consisting of a rigid support ring adapted to fit in fluid-tight relation within a cylindrical bore in the housing. The ring supports a resilient rubber-like sealing element in fluid-tight contact with the outer surface of the relatively rotating shaft or a wear ring supported thereon. Examples of such seals are shown in U.S. Pat. Nos. 4,747,603 and 4,278,261. When seals of this type are operated in an environment where foreign matter such as dust, mud or water may contact the outer surface of the resilient sealing element, it is common practice to provide a secondary seal usually referred to as a dust lip or auxiliary lip, in an attempt to prevent the ingress of such foreign material (dust) into the sealed area between the housing and shaft. Seal assemblies including dust seals of this general type are shown, for example, in U.S. Pat. Nos. 4,243,232; 4,278,261; 4,336,945; and 4,721,312.
While the prior art bearing shaft seals incorporating dust lips have generally been satisfactory for most uses, they have not been entirely satisfactory for use in environments containing heavy concentrations of abrasive and corrosive dust, particularly where inspection of the seal and related equipment cannot readily be made during operation. For example, the wheels on railroad cars are supported on the car axles or shafts for rotation by low friction roller bearings, with seals provided at each end of each wheel bearing to prevent the escape of the grease or oil used to lubricate the bearing and to prevent ingress of contaminants. Such seals are subject to constant and severe vibration while the car is being transported and continuously operate in a hostile environment where dust and corrosive materials from the product hauled, as well as dust, mud and water from the roadbed, present a serious problem because of the tendency of abrasive and corrosive materials to find their way past the seal and contaminate the lubricant. Such contaminant materials tend to be very abrasive to the shaft and/or wear ring, causing premature wear and failure, with the consequent danger of accelerated dust penetration or lubrication loss and damage to the sealed bearing structure.
As pointed out in the above-mentioned U.S. Pat. No. 4,336,945, seals of this type generally employ a so-called hydrodynamic or pumping surface contour in the area of the primary lubricant sealing lip, which pumping surface tends to pump or impel escaping oil back into the sealed area. Any dust particles or the like which penetrate past the dust seal portion may actually be entrained in escaping oil adjacent the primary lubrication sealing area and be pumped back into the sealed bearing cavity. The abrasive action of even small amounts of such dust can increase the bearing friction, thereby causing overheating of the lubricant and ultimate failure of the bearing.
Attempts to solve the problem of dust penetration include providing dual dust lips spaced axially from one another, with the lips dimensioned to contact the shaft and to be deflected outwardly away from the lubricant seal portion when the seal is installed. It should be apparent, however, that where a seal is employed at each end of a bearing which is mounted from one end of an axle or shaft, the desired outwardly deflected arrangement of the dual dust seal lips disclosed in this patent cannot always be assured. Further, a double sealing lip continuously contacting the shaft increases the friction load which not only requires additional power or energy, but also results in additional heat which can result in an overheating of the seal and premature or accelerated degeneration of the elastomer. Heat from seals are a known contributing factor or cause of many hot boxes on rail cars. Even where the temperature of the bearing is not elevated to a dangerous condition, the temperature may rise sufficiently to cause a premature warning to be given from a hot box detector causing a railcar to be unnecessarily pulled from service.
In the normal operation of low friction roller bearings such as used to mount a wheel on a rail car axle, some small amount of lubricant will inevitably leak past the primary lubricant seal lip. Some leakage is desirable to wet the primary lip, and such leakage generally is minimized and controlled by a combination of features including the use of compression members such as an endless coil garter spring ring employed to continuously resiliently urge the lubricant sealing lip into contact with the rotating shaft and the use of the above-mentioned hydrodynamic surface contour on the resilient primary lubricant sealing lip.
Any lubricant weepage past the dust lip will quickly become contaminated with dust particles and will tend to build up on the shaft outwardly adjacent the dust lip. Entrainment of substantial dust particles causes the contaminated lubricant to become abrasive and wear the shaft or wear ring and, to a much lesser extent, the resilient sealing element with which it is in rubbing contact. Such seal and/or shaft ring wear reduces the efficiency of the dust shield and increases the likelihood of ingress of contamination through the primary lubricant seal into the sealed bearing area. Also, ingress of dust particles will ultimately increase wear on the primary lubricant sealing surface and clog the hydrodynamic feature referred to above.
It is, therefore, a primary object of the present invention to provide an improved bearing shaft seal assembly.
Another object is to provide a shaft seal element which includes improved dust sealing features.
Another object is to provide such a sealing element including a primary lubricant sealing area and axially spaced dust sealing area, with the dust sealing area including both a shaft contacting and a non-contacting lip to improve the dust sealing qualities of the assembly.
Another object of the invention is to provide an improved wheel bearing seal assembly for heavy duty vehicles having improved sealing qualities and longer service life.